The present invention provides both a method of controlling a said cooling airflow and apparatus for effecting said control.
Gas turbine engines operate over a varying range of conditions, eg those powering an aircraft are required to run at idle speeds, taxiing speeds of an associated aircraft, take off speeds, cruise speeds and landing speeds of that aircraft. All these regimes require different power outputs which, in order to ensure maximum engine operating efficiency during each regime, must be achieved at maximum design gas temperatures.
Some operating regimes, eg take off and climb of an associated aircraft, generate gas temperatures which make it essential to cool the vanes and rotor blades of the gas turbine engine. Cooling is achieved by introducing compressor driven air to the interior of the vanes and discharging it through the walls thereof, to the gas stream in which the vanes and blades of the turbine lie.
Prior art arrangements always introduce the maximum quantity of cooling air necessary, which is dictated by the speed of rotation of the compressor, which in turn is dictated by the flight regime of the associated aircraft, ie take off or climb or any of the regimes named hereinbefore. In all operating regimes except take off and climb, an excessive supply of cooling air results, to the extent that engine efficiency is impaired.